There are numerous existing systems for removable dental protheses making generally use of couplings of the press-button type one part of which, usually the male part, is fastened onto the jaw of the patient either in the bone or in a valid tooth, and the other part of which, the female part, is fastened in the prothesis. Such coupling devices are for example described in the following patents CH 646.046; CH 646.047; CH 651.462 and CH 651.194.
Most of these devices have the drawback of a too rigid fixing of the prothesis in the mouth, so that under the effect of shocks and efforts due to chewing of the food stuff, it is frequent that after a certain duration the cementing of the male part implanted into a valid tooth or into the jaw bone is loosened or destroyed.
In the device described in the patent CH 597.843 a fixing rider which is elastically deformable is put between the male and female part of the coupling giving a certain smoothness to the fixing of the prothesis. However, during the setting in place and the withdrawal of this prothesis, the resilient deformation of this rider transmits substantial forces to the prothesis. These forces make it necessary to provide important and very solid walls of the prothesis to avoid its deterioration and this increases the weight and the encumbrance of the prothesis in the mouth.
There are further other types of coupling permitting a removable fixing of a prothesis with a certain degree of smoothness which use male or female coupling members made in two parts which are resiliently deformable the one with respect to the other. The drawback of these devices is that the voids and spaces comprised between these two parts fill with detritus or tartar causing a bad hygiene of the mouth and a bad working of the coupling device.
Patent CH 674.926 discloses a coupling for removable dental prothesis which comprises a retention member which is fixed in the mouth, one end of which is formed by a threaded rod whereas the other has the shape of a portion of a sphere and a matrix comprising a rigid casing housing a resiliently deformable mass provided with a void intended to receive this spherical portion of the retention member. This matrix presents means for a rigid and definitive fixation into a prothesis.
The drawback of this type of coupling resides mainly in the fact that the resiliently deformable mass is rapidly weared off and that its characteristics are modified with the aging within the mouth.